1. Field of the Invention
The invention relates to an improvement in the process for preparing primary mono- and diamines by reductive amination of oxo compounds, optionally containing other reducible groups or functions, such as C.dbd.C double bonds, nitrile (and nitro) groups, by a preliminary treatment with ammonia in the presence of catalysts loaded with ammonium ions.
The term "oxo compounds" indicates, as usual, compounds containing carbonyl groups, particularly aldehydes and ketones.
2. Description of the Prior Art
It is already known that saturated and unsaturated aldehydes and ketones can be converted into primary amines with ammonia and hydrogen under elevated pressure and at elevated temperatures using suitable catalysts, for example, those having cobalt and/or nickel and/or iron as the principal components.
The reductive amination of compounds having a low molecular weight and a simple structure is actually accomplished in a comparatively satisfactory manner, but with compounds having higher molecular weight, complex structure or several functional groups a comparatively low space velocity is frequently observed. In that case also, the life of the catalyst is frequently unsatisfactory. These two characteristics are affected by a rather extensive formation of by-products, particularly when the formation of cyclic structures is favored. Such by-products not only reduce the yield of the reaction but often significantly reduce the overall yield because of difficulties in workup or purification of the desired amines. Yields below 80%, sometimes even below 50%, are observed, for example, in the production of benzylamine from benzaldehyde, furfurylamine from furfuryl alcohol, pentanediamine from the corresponding cyanoaldehydes, 3,3,5-trimethylcyclohexylamine (TMCA) from isophorone (3,5,5-trimethyl-2-cyclohexen-1-one) or 2,2,6,6-tetramethyl-4-aminopiperidine (triacetonediamine, TAD) from 2,2,6,6-tetramethyl-4-piperidone (triacetoneamine, TAA) and, particularly, in the production of 3-(aminomethyl)-3,5,5-trimethylcyclohexylamine (isophoronediamine, IPD) from 3-cyano-3,5,5-trimethylcyclohexanone (isophoronenitrile, IPN). In the last mentioned reaction, for example, there are formed not only the by-product 3-(aminomethyl)-3,5,5-trimethylcyclohexanol (isophoroneamino alcohol, IPAA), but a large number of by-products arising from elimination of HCN, cyclization, side reactions and further reactions of intermediate products. A mixture of compounds, characterized as the so-called peak 7 in gas chromatography, can be separated only with especially great difficulty. This mixture of compounds causes a distillation loss of approximately 1% IPD per 0.1% of the peak 7 mixture in the purification of IPD to the specifications prescribed, for example, for the production of polyamides. Similar undesirable by-products also arise in the reductive amination of other oxo compounds. Accordingly, there has been a need to find a procedure by which the desired amines would be obtained in a distinctly higher yield and at the same time by a process which would be economical on industrial scale.